Lantana camera is indigenous to South and Central America, but was widely introduced as an ornamental plant and is now considered a weed in about 50 countries worldwide. In Africa it has invaded much of sub-Saharan Africa, forming dense thickets that displace natural communities and compromise agricultural productivity
Weed of many colours
Lantana is a highly variable species, with hundreds of different cultivars that differ in appearance and in their tolerance to environmental conditions. The plant may occur as a compact shrub or a scrambler more than 5 metres high, and is often used as a hedge plant because that makes it such a menace when it invades agricultural land and forestry plantations. The thickets disrupt access of livestock to grazing and water, interfere with farming and forestry activities, and increase the intensity of fire. By e n c roaching onto pastures, they reduce the carrying capacity and productivity of agricultural land. Lantana is also a weed in a variety of crops, including coffee, coconuts, cotton, bananas, pineapples and sugarcane.
Furthermore, the entire plant is toxic and ingestion of the leaves and fruit can poison cattle and sheep, exhibiting as increased sensitivity to sunlight. The soft skin of the nose, eyes, ears and lips become covered in sores that make eating and breathing painful, causing the animals to lose condition or even die. In some areas, lantana thickets provide a breeding ground fo tsetse flies, which transmit the parasitic trypanosomes that cause nagana, an animal form of sleeping sickness.
Little else can grow in lantana thickets because the plant releases chemicals into the soil to prevent other plants f rom germinating. The absence of an understorey community to provide groundcover results in increased erosion, particularly on steep slopes. By excluding other species the thickets reduce plant biodiversity and change the composition of associated animal communities.
Lantana is able to spread rapidly once introduced to an area as the seeds are widely dispersed by birds eating the fruit, and are sometimes also washed from infested areas during floods, causing sudden invasions downstream.
Lantana is difficult to control, as it will coppice and form denser thickets if it is simply slashed and left. Mechanical control is labour-intensive, and should only be used on its own for seedlings and small, individual plants. These can be uprooted by hand-pulling when the soil is moist or first loosened with a hoe, pick or fork. Uprooting of large plants or dense thickets is not recommended as it results in soil disturbance, increasing the risk of soil erosion and re-infestation by lantana seedlings and other opportunistic weeds.
A combination of mechanical and chemical control is best used for larger plants and dense thickets. Top growth should be cut away and the plant felled close to the ground, after which the stump should be treated with a registered herbicide. Foliar application of herbicides is suitable for small lantana plants and re-growth. But for large, dense bushes it is expensive and not very successful, since the maximum height that can be reached using a knapsack sprayer is about 2 metres. All forms of control should be followed by revegetation, ideally with indigenous groundcovers, to prevent seedlings from forming new thickets. It is also essential that ongoing follow-up work, involving handpulling of seedlings and spot-spraying of regrowth, is conducted at least annually.
A long history of biological control
Internationally, there is a long history of biological control of lantana, but there are few completely successful examples. In South Africa at least 12 biocontrol species have become established on lantana, yet it remains one of the c o u n t ry ís most vigorous invasive weed species. The biocontrol agents include two leaf-sucking bugs, two leaf-mining beetles, a seed-feeding fly, a leaf-mining fly, two leaf-feeding moths and a flower-feeding moth.
The most promising agent is the lantana mirid Falconia intermedia, first released in 1999. Both the adults and nymphs are sapsuckers that feed on the leaves, removing the chlorophyll that is vital for photosynthesis, which causes white specks on the upper surface of the leaf. Severe feeding damage can result in the entire plant taking on a silvery white appearance and losing leaves prematurely. This starves the plant of resources and limits
its capacity to produce flowers, new leaves and shoots. By reducing the plantís aggressive growth rate, the mirid allows other species to compete with lantana for space.
The latest biocontrol agent to become established is a leaf-mining fly, the herringbone leafminer Ophiomyia camarae. Owing to its short generation time and high egg-production rate, it has the potential to increase rapidly in numbers. During her 18-day lifespan the female lays approximately 92 eggs, depositing them singly inside the veins of lantana leaves. When the eggs hatch, the larvae feed on leaf tissue by mining through the leaf for 8 to 10 days before pupating. The mining damages the fluid transport system of the leaf, causing it to drop prematurely.
By suppressing growth and reproduction of lantana, biological control will not only reduce the cost of conven-tional control, but also help decrease the invasive potential of the weed.
Reference: Wittenberg R. & Cock M.J.W. Invasive Alien Species: A Toolkit for Best Prevention and Management Practices Invasive Alien Species: A Toolkit for Best Prevention and Management Practices